This invention relates to a pulse generator combined with a micromotor, that is an electric motor having very small size and capacity.
A pulse generator combined with a micromotor is used to produce a pulse corresponding to the number of revolutions of the micromotor and supplied to various control circuits. Typical construction of such combination is shown in FIGS. 1 and 2. In these figures, the micromotor comprises a rotor 1 secured to a rotary shaft 2, a commutator 4, brushes 5, a metal casing 6, and an end cover 7 made of synthetic resin.
As shown in FIGS. 1 and 2, the conventional pulse generator comprises a rotary magnet 8 secured to the shaft 2 of the micromotor and having a plurality of magnetized poles about the periphery, a stator coil 9 surrounding the rotary magnet 8, and a pair of stator yokes 10 and 11 respectively having magnetic teeth 10a and 11a which are arranged alternately along the inner peripheral surface of the stator coil 9.
The pulse generator is desired to increase the number of magnetic poles of the rotary magnet 8 in order to increase the detection frequency. As it is necessary to maintain a definite pole pitch spacing, in order to form a plurality of poles, it is necessary to increase the outer diameter of the rotary magnet 8. Furthermore, since the width of the magnetic poles is limited by machining and dimensional accuracy, it is also impossible to make small the stator yokes 10 and 11, whereby overall size of the pulse generator increases. Usually, the stator yokes 10 and 11 are prepared by working magnetic plates, and particularly since their magnetic teeth 10a and 11a are formed by stamping and bending there is a problem of accuracy due to nonuniform bending or inclination of the magnetic teeth.